I found this...
“In all the time that I’ve spent in (8 yrs.), the usual minimum for anyone with an M16 or M4 is 210 rounds (7 x 30 rds mags.) For the M249 SAW, the basic load is 400 rounds (2 x 200 rds drum or 4 x 100 rds.). For the M240, it’s usually the same as the SAW.
Source(s):
U.S. Army Veteran (2001 - 2009)”
http://answers.yahoo.com/question/index?qid=20091018115954AAMtSTq
Pretty much what I remember from the 60’s, only we used the M-60, not the M240.....favorite was carry as much as you could and not crap out..........